in potential between the two live legs, any imbalance of the load will be supplied by a current in the neutral, giving substantially constant voltage across both groups. The total current carried in all three wires (including the neutral) will always be twice the supply current of the most heavily loaded half.

For short wiring runs limited by conductor current carrying capacity, this allows three half-sized conductors to be substituted for two full-sized ones, using 75% of the copper of an equivalent